Transmission regulation in cable circuits



Dec. 8, 1931. K. w. PFLEGER TRANSMISSION REGULATION IN CABLE CIRCUITS Filed Aug. 16, 1929 5 Sheets-Sheet 1 ...nun nu".

ATTORN EY mvENToR E er Dec. 8, l1931. K. w. PFLEGER 1,835,080

TRANSMISSION REGULATION IN CABLE CIRCUITS Filed Aug. 1e, 1929 :s sheets-sheet 2 .30.00 4000 5000 E'equency, cyclesper .sewnd f7 f /z-Zs per sec.

Step

.Step 7 INVENTOR BY y@ ATTORN EY Dec. 8, 1931.

K. w. PFLEGER l835,080

TRANSMISSION REGULATION IN CABLE CIRCUITS 5 Sheets-Sheet 3 Filed Aug. 16, 1929 7000 .Treguencycycles pera-@cond Ste 1510 Ste +4 I're uen.: yc es per second 00l sa 0'@ 1bn 200 4000 6000 0000 INYENTOR .We er ATTORNY Patented Dec. 8, 1931 UNITED j STATES PATENT OFFICE KENNETH W. PFKIIIEGfrElR., OF ARLINGTON, NEW JERSEY, ASSIGNOR T AMERICAN TELE- PHONE AND TELEGRAPH COMPANY, A CORPORATION 0F NEW YORK TRANSMISSION REGULATION IN CABLE CIRCUITS l vApplication led August` 16, 1929. Serial No. 386,436.

This invention relates to methods of and means for regulating the transmission over telephone or carrier telegraph circuits, and

kmore particularly to regulation suitable to program transmission over telephone cable circuits.

Cable circuits are affected as to transmission characteristics by changes of temperature, the transmission characteristics being a function of the frequency of the transmitted Current. In certain types of cables, at least, field measurements show that an increase of temperature, for instance, produces an increase of transmission loss at low and intermediate frequencies and that this change of transmission varies with frequency change, passing through zero at a certain high frequency and becoming a negative increment in loss at the higher frequencies.

The principal object of the invention is to provide for transmission regulation which will offset the variations mentioned above and produce a substantially fiat transmission characteristic over the normal range of temperatures and a wide range Vof frequencies.

In general I accomplish the above-stated object by associating resonant shunt circuits with a potentiometer in the transmission line, and providing for impedance adjustments in accordance with the regulation required.

The invention will be clearlyunderstood when the following description is read with reference to the accompanying drawings, of which* Figure 1 shows d iagrammatically a simple circuit illustrating the principles of the invention;

Figs. 2, 3 and 4 show diagrammatically'the effective circuits produced by adjustment of the arrangement of Fig. l to meet various transmission conditions; f

`Fig- 5 shows curves illustrating the effect i of the circut adjustments of Fig. l;

Figs. 6, and 8 show the effect on the transmission of temperature and frequency changes and indicate the correction to be introduced; and

Fig. 9 shows diagrammatically a desirable form of apparatus embodying the invention as applied to a vacuum tube repeater.

With reference, first, to Fig. l of the drawings, there is shown a circuit including a potentiometer controlled by a switch S1, which has three positions, step 0, step -l- 1 and step -1. These steps have relation to changes in temperature of a certain number of degrees, measurements being made on a certain cable circuit of fixed length. Step 0 may correspond to the average temperature affecting the circuit. While certain impedance elements are shown as pure resistances, and the resonant shunts are shown as composed of an inductance and a capacity in series, it will be understood that this specific disclosure is merely for the purpose of illustration of the methods and means of the invention. Furthermore, the values assigned tothe various elements are merely for the purpose of exposition through equations.

The potential impressed on the circuit is assumed to be 1 volt, and the values of the resistances in ohms are indicated. For the purpose of simplification, the impedances of the shunts are designated as al and z2. With switch S1 on step 0, switch S2 open and switch S3 open, the received voltage (En) will be designated E0; with S1 on step +1, S2 open and S3V closed, the received voltage is En; and with S1 on stepv -1, S2 closedand S3 open, the received voltage is E l. 'The discussion will be clarified by reference to Figs. 2, 3 and 4 which show these three circuit conditions, respectively.

With particular reference, now, to Fig. 2, let R- represent the total resistance of the circuit and R0 the resistance from a to lb. which is the volta-ge across the circuit from V227" @di 7131 tir-:2n times the frequency in cycles per second, it is found that Equations (A) and (B) give the curves A and B, respectively, of Fig. 5 of the drawings, transmission being plotted as ordinates and frequency as abscissaa.

It will be understood in general, and it will appear specifically hereinafter, that a greater number of steps may be-and usually will be-used, and that .alk and 22 may be varied for each step.

It appears from the above discussion, with reference to the drawings, that the receiving impedance may be nearly infinite as in the case of a vacuum tube grid), but that this feature is not essential.

Figs. 6 and 7 of the drawings show some of the transmission variations brought about in a cable circuit by change of temperature and change of frequency, and indicate the correction which approximates the ideal result 'of constant transmission. The field measurements are expressed in terms of a cable circuit having a length of 17 8 miles; an average or step-zero temperature of degrees Fahrenheit is taken; and each step corresponds to a change in temperature of about 5.4 degrees Fahrenheit. Only the results for the even steps are shown, and the figures are concerned with the variation with frequency in the range over one thousand cycles per second.

In Fig. 6, a curve is shown corresponding to each of the even plus steps, transmission losses in Z6 being plotted as ordinates and frequencies in cycles per second as abscissae. These curves show the variations of gain or loss with respect to frequency which it is desired that the regulating system should give, the curves being determined by measurements made on existing cable systems. rIlhe dots. crosses and circles indicate the variation in gain which. it has been found from measurements made on a particular regulator, may be introduced to give an approximate compensation for the transmission variation. It is seen that these variations give a very close approximation to the ideal variations indicatedby the curves. It will be noted that at the higher frequencies, the transmission loss becomes negative, and accordingly losses must be introduced at those frequencies to give constant transmission.

Fig. 7 shows the transmission loss variation with frequency for the even minus steps and, like Fig. 6, which covers the positive steps, indicates the variation of gain which must be introduced for correction.

In Fig. 8 four curves are shown, two for the plus steps and two for the minus steps. T hese curves show on a scale different from that of Figs. 6 and 7 the gain which is to be introduced to give a substantially flat transmission characteristic. It Will'be noted that in this figure, the Alower as well as the higher frequencies are covered.

It remains to show by way of illustration a regulator for producing a compensating variation such as that indicated in Figs. 6, 7 and l8. The specific case chosen for illustration is an arrangement including a potentiometer designed to operate .between the stages of a vacuum tube repeater. This arrangement is shownin Fig. 9 of the drawings.

The vacuum tubes T1 and T2 are two tubes of a4 repeater. At the right of Fig. 9, in association with the grid of the tube T2, a poten- 'on each side of the series resistance R2.

It will be understood, ofcourse, that the potentiometer contacts are adjusted, in any suitable manner, between step +10 and step 10 in accordance with the temperature affecting the transmissioncircuit. Likewise,

the resonant shunts are varied by switches shown on the drawings and designated step 0, steps +1 to +10 `and steps +1 to -10.

On the positive steps a resonant shunt, including in series one or more of the upper bank of condensers, shown to the left of the switches, and the inductance indicated at Il, is connected from step 10 of the potentiometer over point Y to ground. The tuning of the shunt is provided for as indicated above, the shunt impedance being made suitable to the given positive step of the potentiometer. Thus, the current in the potentiometer is reduced at high frequencies, and the voltage acting on the grid of tube T2 is diminished, giving the desired characteristics on the positive steps.

On the negative steps ay different shunt, including in series one or more of the lower bank of condensers shown to the left of the switches and the inductance I2, is connected from step -10 of the potentiometer to the point X. This shunt, like that discussed above, is varied by operation of the switches to give a suitable impedance shunted across both the upper portion of the potentiometer and the resistance R1. This results in the reduction of the load impedance of tube T1, and the current delivered by this tube increases at high frequencies. Accordingly, the voltage across the resistance R2 is increased, and as a result, when the regulator isfoirthe' negative steps, the voltage acting ,i

on the grid of tube T2 is increased.

.Y It-Will, 'of course, be :understood from an examination of Fig. 9 and-from the more general discussion appearing hereinabove that on step both the shuntsv described above and Vthe shunt impedance by Vcorresponding' Y '35 potentiometer, the method of transmission are open.l Inorder that the transmission frequency characteristics of the regulating stage of the repeater may beflat .When the potentiometer 'is on step 0, a regulator equalizer netWorkRE should be locatedV in the inter-y ystage circuit of the regulatingrepeater between the regulating potentiometer andthe apparatus from Which it receives its current,

71VAugust, 1929. t v Y 'KENNETHVQ PFLEGER. j

,5. In a transmission circuit, a potentiom#V eter, a variable impedance in shunt with said potentiometer, and means for adjusting said.

potentiometer and said shunt impedance by definite and corresponding stepsto give a fiat transmissionY characteristic over a Wide range of temperatures and frequencies.

In testimony whereof, I have signed myl name'to thisspeciiication this 15th day of thefimpedanceof the elements of the"equal s izer beingchosen to produce the desired result. i Y 1 While the invention has been described speciiically for thepurpose oilV illustration, it is toy be understood that many changes may be made from the specific form described VWithin the scope of the appended claims.

What is claimed is:

1.91111Y a transmission circuit including a .Y potentiometer, the method of transmission Y regulation Which. consists in associating a yvariable impedance in shunt With the potentiometer and adjusting the potentiometer steps vin accordance with temperature changes affecting the circuit, to'givelaflat transmis-- `sion characteristic over the Vrange of temperatures and a Wide rangeof frequencies.`

2.111 al transmission circuit including a regulation which consists in adjusting the tive at certain other frequenciesfor the same potentiometer setting.

3. In a circuit iiicludinga potentiometer, fthe `method of regulating'the transmission y of alternating.currentsover the circuitvvhicli consists in determining the transmission variations YWith changes of temperature and With changes of frequency, including the range from 3,000 to 8,000 cycles per second,'intro ducing an auxiliary impedance'in shunt With thepotentionieter, and adjusting the potentiometer and the shunt impedance by definiteV steps .corresponding to temperaturev changes Y *to produce transmission variations compen- Satine;V forthose caused bythe temperature Vto and frequency changes.

f4. Ina transmissionfcircuit, a potentiometer adjustableindenite steps, andva varia-ble impedance in shunt with said potentiometer and adjustable in definite steps corresponding to thel potentiometer steps, Wherelby-theremay be produced-*inthe circuit `a Aflat transmission characteristic Vover a Wide 1ra-nge oftemperatures and frequencies. 

